This invention relates to downhole devices for subsurface wells or bores, and more particularly to an anti-extrusion ring assembly for downhole packing devices used in elevated temperature and pressure environments.
Expandable packer assemblies are commonly used in the oil and gas industry to seal or close off the annular area between a well bore casing and a drill pipe or tubing. The packer assembly includes a sealing sleeve or packer that is cylindrically shaped and typically has a smaller outer diameter as compared to the inner diameter of the particular casing to be sealed, and is thus easily inserted and positioned within the annular area. Expandable packers may, for example, be constructed of rubber or some other elastomeric material and include a central axial bore through which various types of tools or tubing may be inserted. A mandrel may, for example, be located in the axial bore of the packer, wherein the packer and mandrel are positioned within the casing at a predetermined location and/or depth, in the case of a subterranean well. Activation of the mandrel in combination with upper and lower slip members creates axial compression setting forces which are applied to the axial ends of the packer. The axial compression setting forces cause a reduction in the axial length of the packer and a corresponding increase in the packer outer diameter. As a result, the packer seals against the inner surface of the casing to effectively seal the annular area. An anti-extrusion ring, typically in the form of a split metallic ring, is positioned between the packer and each of the upper and lower slip members. The anti-extrusion rings are intended to prevent extrusion of the packer under elevated temperature and pressure conditions that would otherwise destroy the packer and/or the seal between the packer and the inner wall of the casing.
During use, it may become necessary to remove the packer for various reasons, typically by drilling through the packer and the metallic anti-extrusion rings. Although the elastomeric packer material is relatively easy to drill through, removal of the metallic rings has proven to be more difficult.
It is therefore an object of the present invention to provide an anti-extrusion ring for a packer assembly that is relatively easy to remove, even after the packer assembly has been set in a casing or other tubing.
It is a further object of the invention to provide an anti-extrusion ring for a packer assembly that is multi-segmented.
According to the invention, an anti-extrusion ring for a packer assembly comprises first and second ring portions that are divided into a plurality of discrete arcuate segments. The segments are adapted for movement between a retracted position wherein each segment is in contact with adjacent segments, and an expanded position wherein gaps are formed between the segments. At least one of the ring portions is adapted to face a resilient sealing sleeve of the packer assembly. The first ring portion is circumferentially offset from the second ring portion such that at least one of the first and second ring portions extends across the gaps during movement of the segments toward the expanded position. In this manner, extrusion of the sealing sleeve through the gaps is prevented.
Further according to the invention, a downhole packer assembly for use in a well bore comprises an elongate mandrel adapted for positioning in the well bore; an expander adapted for sliding movement along the mandrel; a resilient sealing sleeve disposed around the mandrel for engaging the well bore; and at least one anti-extrusion ring disposed between the expander and the sealing sleeve. The at least one anti-extrusion ring comprises first and second ring portions that are divided into a plurality of discrete arcuate segments. The segments are adapted for movement between a retracted position wherein each segment is in contact with adjacent segments, and an expanded position wherein gaps are formed between the segments. At least one of the ring portions contacts the sealing sleeve. The first ring portion is circumferentially offset from the second ring portion such that at least one of the first and second ring portions extends across the gaps during movement of the segments toward the expanded position. In this manner, extrusion of the sealing sleeve through the gaps is prevented.
Other objects and advantages of the invention will become apparent upon reading the following detailed description and appended claims, and upon reference to the accompanying drawings.